Bath for electroplating silver



. 2,777,810 7 BATH FOR ELECTROPLATING SILVER Barnet D. Ostrow, North Bellmore, N. Y., assignor to. Elechem Corp., Jersey City, N. J., a corporation of New Jersey No Drawing. Application October 3, 1956, Serial No. 613,610

12 Claims. (Cl. 204-46) The present invention is directed to electroplating, more particularly to a composition of a bath for depositing silver from cyanide solutions. This application is a continuation-in-part of Serial No. 487,705, filed February 11, 1955, entitled Bath for Electroplating Silver, and of Serial No. 242,041, filed August 15, 1951, entitled Electrolytic Bath for Copper and Silver (abandoned).

In the abandoned application of Weiner, A. P. C. Serial No. 351,241, there is described a production of bright coatings from silver cyanide solutions by the use of selenites in conjunction with proteolytic compounds, together with an alkali metal thiosulphate or thiocyanate. In the operation, there was used a high concentration of selenium, up to 20 grams per liter. The amount. of the sulphur compound used was up to 50 grams per liter. Such sulphur compounds had the disadvantage of breaking down during the operation of the bath, with a resulting adverse effect on the current density range. If the sulphur compound was omitted, the characteristics of the bath at low current densities was very poor. Also the high 2,777,810 Patented Jan. 15, 1957 is apt to be some dullness in the low current density areas but excellent results are obtained, nevertheless. In applicants bath it is, unnecessary to have present such sulphur compounds as thiosulphates or thiocyanates.

concentration of selenium also had an adverse efliect in a the low current density range whereby the deposit in such areas was dull and whitish and could only be overcome by the addition of the aforesaid sulphur compounds, which in themselves introduce difiiculties in the bath. It has also been proposed to add to the silver bath containing the selenite, potassium nitrate, but deposits obtained from such a bath were even less bright than those proposed by Weiner. Y

The. present invention is intended and adapted to overcomethe difficulties and; disadvantages inherent in the prior art, it being among the objects of the present invention to provide a silver cyanide bath which is capable of depositing silver, which is highly ductile, the deposits being bright to brilliant, while using relatively low concentrations of addition agents.

It is also among the objects. of the present invention to provide a bath which deposits silver uniformly over a widerange ofcurrent densities, which deposits have an improved resistance against tarnishing.

It is further among the objects of the present invention to provide a bath for the purposes described which is stable over long periods of, operation thereof.

In practicing the present invention, it has been found that selenium compounds having a valence of 2 when added to a silvercyanide bath, impart far better operating characteristics than the selenites proposed in the prior art. It has, been found that optimum results are obtained when the selenium is present in amounts from .0001 to .01 grams per liter. Preferably the concentration of selenium in such compounds should not, be over .005 gram per liter whereby the best results are obtained. From present knowledge, it is believed that the optimum concentration of. the selenium should be about .001 to .003 gram per liter, as a result of which a bright plating range from 0 to 70 amperes per square foot is obtained. When .01 gram per liter of such selenium compounds are used, there The compounds of selenium used inaccordance with the present invention are both organic and inorganic but it is'essential that in such compounds the selenium has a valance of -2. Among such-compounds are the soluble selenocyanates, solenoureas, selenophenols, selenides and selenosulphites. 7

It has also been found in accordance with the present invention that improved results'may be obtained by the addition of soluble lead or antimony saltsrin conjunction with said selenium compounds. The concentration of antimony in the bath ranges generally from 0.1 to 1.0

- gram per liter and excellent results are obtained if the concentration is within the range of .15 to .40 gram per liter. When lead is used as an addition agent, it is present in the range of .001 to .10 gram per liter. The addition of salts of these metals has the highly desirable effect of producing a. more uniformly bright deposit. The use of the. antimony compounds has advantages over the use of lead compounds in that a better type of brightness is obtained. in the deposit and the bath is less sensitive to fluctuation of brightness than when selenium alone is used or when selenium and lead are used in the bath. The deposits are uniform and the. addition agents are stable, thereby providing a highly practical commercial type of bath. 7 V v The following are examples of the operation of the present invention and in the formulas given below, the quantities of the constituents are expressed in grams per liter of water; e

Example! The following composition is provided: AgCN 30.0 Total KCN 50.0 KzCOs 30.0 So as KzSe- .001 KSb gluconate 1.0 Cetyl betaine .04

p The bath is operated at current densities ranging from O to 60 amperes per square foot with continual agitation. The temperature is. maintained between and F. The deposits obtained are bright over substantially the entire range of current densities.

The current densities range from 0 to amperes per square foot, with agitation, and the maintenance of the temperature of the bath between 70 and 80 F. The deposits are bright over practically the entire range of current densities.

Example 3 The following composition of bath is provided: AgCN 45.0 NEICN 72.0 NazCOs 15.0

Se as selenourea .002 70 Free NaCN 60.0 NaSb gluconate 1.0

Plating is conducted at temperatures between 70 and 100 F. with agitation, with current densities from to 40 amperes per square foot; the resulting deposits are brilliant.

The plating is conducted at 70-75 F. with a current density of to 40 amperes per square foot with continuous agitation. The plate is very brilliant and the results are excellent.

Example 5 AgCN 30.0 Total KCN 50.0 K2CO3 30.0 Selenourea .003 KSb tartrate 0.5 Polyethylene oxide 400 Laurie acid salt .01

The plating is conducted under the same conditions as set forth in Example 4 and the results are equally as good.

Example 6 The bath contains the following constituents which include the use of lead in the bath:

AgCN 30.0 Total KCN 50.0 KzCOs 30.0 Se as K2Se .001 Pb tartrate .06 Cetyl betaine .04 Rochelle sal There is maintained a current density from 0 to 60 amperes per square foot with agitation and maintaining a temperature between 75 and 85 F. The deposits obtained are bright.

It has also been found that when the bath contains both selenium with a valence of 2 and soluble antimony compounds, the deposits are more brilliant when the alkali metal cyanide used contains sodium than when the bath contains only potassium as the alkali metal. It has also been found that brighter deposits are obtained in a bath containing potassium as'the alkali metal when there is present sodium to the extent of at least 25% of the alkali metal ions in the bath.

Since in silver plating from alkaline cyanide solutions, it has been found that when the alkali metal is entirely potassium, the results in operation are more desirable than when the alkali metal is entirely sodium because such potassium-containing baths permit operation at higher current densities for a given concentration of metal and free cyanide, and temperature, and such baths tolerate higher concentrations of carbonates. According to the present invention, it is possible to retain all of the advantages of the potassium ions in the bath and obtain the full operational characteristics thereof when sodium ions are also present. This has the added advantage that the deposit retains the inherent brightness of the sodium-containing-baths. The following examples illustrate the desirability of utilizing a mixture of sodium and potassium ions in the bath.

4 Example 7 The following composition is provided:

AgCN 45.0 NaCN 20.0 KCN 50.0 Se as KCNSe .001 Rochelle salts 22.0 KSb tartrate 1.0 Na lauroyl sarcosinate 0.75

The current density range is from 0 to 75 amperes per square foot. Agitation is used and plating is conducted at room temperatures.

Example 8 The bath composition is as follows:

AgCN 52.5 KCN 40.0 NaCN 35.0 KaCOs 15.0 KSb gluconate 1.0 Se as selenour .002 p-Tertiary-octyl-phenoxy-acetylglycine 1.0

Current densities ranging from 0 to 60 amperes per square foot are used; the plating is conducted at room temperatures and agitation is use The invention also contemplates combinations of selenium having a valence of 2, with the all potassium type of silver cyanide plating baths. In such cases brighter deposits are obtained by introducing into the bath a soluble thiouracil. Such addition agents are used in amounts ranging from .005 to 3.0 grams per liter and they have the following structural formula:

The thiouracils probably act as purifiers and they are stable over long periods of time of operation. They do not break down or give any harmful effects on the deposit, contrary to experience with prior art sulphur compounds. Once the bath has been broken in, no replenishment of the thiouracils in the bath is required, except if the bath becomes contaminated. These compounds may be used in a bath containing not only selenium having a valence of 2 but also those baths containing in addition either antimony or lead in soluble form. Excellent results are obtained when the thiouracils are used in the presence of selenium having a valence of -2 alone without the addition of lead or antimony. The following are examples of this type of bath.

Example 9 The bath has the following composition:

AgCN 45.0 KCN 74.0 KaCOa 30.0 Se as K selenosulphite .001 2-thiouracil K sal 0.10 p-Tertiary-octylphenoxyacetylglycine 1.0

The operation is conducted at 70 to F. with agitation and at current densities ranging from 0 to 100 amperes per square foot.

vermin 1 Example n v I The composition of-the bat-h is as mm; I AgCN I 40. 0 KCN 64.0 KaCOa 15.0 Se as KCNSe .0007 2-thiouracil NH4 salt- 0.10 KN-lauroyl sarcosinate 1.0

Plating is conducted at temperatures from 70 to 100 F. with agitation and at current densities ranging from 0 to 90 amperes per squarefifoot.

Example "1 1 The bath has the following composition:

AgCN 60.0 KCN 86.0 KzCOs 30.0 Se as selenophenol .002 2-thiouracil Na 0.10 Na N-dodecyl-N-hexylphthalamic acid 1.0

The temperatures of the bath are maintained at 75 to 95 F., agitation is used and current densities range from 0 to 90 amperes per square foot. In Examples 9, l0 and 11, certain wetting agents are used. However, other wetting agents may be substituted for the above named compounds, such as sulphated castor oil, with good results.

Applicant has tried many other selenium compounds in this type of bath and without exception, those with a valence of -2 produce the eminently satisfactory results. Some of the compounds which applicant has determined are suitable for this purpose, are listed below:

Selencyanides (selenocyanates):

Na seleno-isocyanate K-selenocyanide NOa-phenyl selenocyanide Selenides:

Na and K monoand di-selenides Diamine-diphenyl-di-selenide NazSe:

NazSe Selenoacids and salts (organic):

Selenoacetic Selenopropionic Selenoglycollic Selenobenzoic Diselenobenzoic Selenotartaric Selenocitric Seleno oxalic Selenoacids and salts (inorganic):

Na selenophosphite K selenostannate Na selenopersulphate K monoselenothiosulphite K seleno diphosphite Selenoamines and amides:

Ethylamineethyl-diselenocarbamate Selenourea K-selenoamide Seleno xanthates: K-selenoxanthate Selenols (alcohols):

Ethyl selenol Ethylene selenoglycol Selenophene:

Selenophene 2-sulphonic acid Selenophene 2-selenic acid Selenoazoles 2-selenothiazoline 2-seleno selenazoline Z-methylbenzo selenazole The applicant has made tests on a range of compounds, the scope of which is indicated "by the list appearing above and he has been unable to discover any selenium compound in which selenium has a valence of 2, which does not produce satisfactory results.

Although the invention has been described with the specific mention of certain compounds of selenium having avalen'ce of 2, other such compounds are contemplated. For instance, both the inorganic and organic selenides and selenocyanates are applicable, as well as soluble selenophosphites, selenothiosulphites, and selenoazoles. Reaction products of selenium metal with certain acids to form soluble selenium compounds are also included. The proportions of the constituents givenin the specific examples may be varied in accordance with established practice. c

- I claim: I

1. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing .a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter.

2. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence.

of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a soluble compound of a metal taken from the class consisting of lead and antimony in an amount of .001 to 1.0 gram per liter.

3. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a soluble lead compound in an amount of .001 to .10 gram per liter.

4. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in Which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a soluble antimony compound in an amount of .01 to 1.0 gram per liter.

5. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a soluble antimony compound in an amount of .15 to .40 gram per liter.

6. An electrolytic bath for depositing silver compris-,

ing an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a thiouracil in an amount of .005 to 3.0 grams per liter.

7. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a thiouracil in an amount of .005 to 3.0 grams per liter, said bath containing alkali metal cyanide, at least part of said metal being potassium.

8. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a thiouracil in an amount of .005 to 3.0 grams per liter, said bath containing alkali metal cyanide, all of said metal being potassium.

9. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter, said bath con: taining alkali metal cyanide, said alkali metal. being sodium to the extent of 25 to 100% of the total alkali metal present. I

10. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter, said bath containing sodium and potassium cyanides.

' 11. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of 2, the amount of selenium present in said bath being .0001 to .01 gram per liter together with a soluble antimony compound in an amount of .01 to 1.0 gram per liter, said bath containing alkali metal cyanide, said alkali metal being sodium to the extent of 25 to 100% of the total alkali metal present.

12. An electrolytic bath for depositing silver comprising an aqueous solution of silver cyanide containing a soluble selenium compound in which the selenium has a valence of -,-2, the amount of selenium present in said 5 bath being about .001 to .003 gram per liter.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES 1 Serial No. 351,241, Weiner (A. P. C.), published May 15 18,1943. Weiner, A. P. c. 351, 241, May 18, 1943.

Schaefer et 211.: Proceedings American Electroplaters Society, 1943, pp. 29-31. 

1. AN ELECTRLYTIC BATH FOR DEPOSITING SILVER COMPRISING AN AQUEOUS SOLUTION OF SILVER CYANIDE CONTAINING A SOLUBLE SELENIUM COMPOUND IN WHICH THE SELENIUM HAS A VALENCE OF -2, THE AMOUNT OF SELENIUM PRESENT IN SAID BATH BEING .0001 TO .01 GRAM PER LITER. 